Vulnerability of buildings to blast loads and progressive collapse

This study is intended to contribute to the understanding of the behaviour of buildings when subjected to blast loads, and to assess the potential for progressive collapse when columns are lost or severely damaged due to blasts. The objective of the study is twofold, i.e., (i) to investigate the performance of reinforced concrete frame buildings subjected to blast loads, and (ii) to assess the vulnerability of such buildings to progressive collapse. Two buildings designed for Ottawa in accordance with the 2005 edition of the National Building Code of Canada were used to achieve these objectives. One of the buildings was designed as a moderately ductile, and the other one as a ductile frame building. For the purpose of the first objective, nonlinear time history analyses were conducted to the moderately ductile building for a number of bomb blast scenarios. Blast loads resulting from detonations of 125 kg, 250 kg, and 500 kg TNT at distances of 5, 10, 15, 20, 25 and 30 m from the building were used in the analysis. The performance of the building was assessed by considering the interstorey drifts, displacement ductilities, and curvature ductilities obtained from the analysis. The results from the analyses showed that the building could be severely damaged and even could collapse when subjected to blast loads due to bomb detonations at distances smaller than 15 m from the building. Regarding the second objective, both the moderately ductile and the ductile buildings were analysed following the guidelines for progressive collapse analysis and design, prepared by the U.S. General Services Administration (GSA). Columns were removed at the first storey of each building. The following three cases were considered: (i) exterior column removed, (ii) corner column removed, and (iii) interior column removed. Elastic static analysis was conducted for each of these cases using 3-D models, and applying loads as required by the GSA guidelines. The demand/capacity ratios obtained from the analysis, and the GSA criteria were used for the assessment of the vulnerability to progressive collapse. The results showed that the ductile building is much more vulnerable to progressive collapse than the moderately ductile building